JP3534367B2 - Wastewater treatment method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the treatment of wastewater, and more particularly to a wet oxidation method and apparatus for oxidizing and decomposing wastewater containing organic pollutants in a high pressure reactor.

[0002]

2. Description of the Related Art Conventionally, organic sewage, especially biodegradable C
In the treatment of OD (chemical oxygen demand) -containing sewage and activated sludge, oxidants such as oxygen and hydrogen peroxide are excessively added under conditions of high temperature, high pressure and powdered oxidation catalyst addition in a high pressure reactor. A wet oxidation method for oxidatively decomposing organic pollutants in wastewater is known. However, in the conventional wet oxidation method, when the water to be treated has a high hardness, if the treatment is carried out in a temperature range of 120 ° C. or higher, the hardness component such as calcium in the water to be treated becomes supersaturated and the inner wall of the reactor is overheated. , And so-called scale is generated. If the scale is grown as it is, there is a problem that the effective volume of the reactor is reduced, and the treatment eventually fails, and it is extremely difficult to remove the scale once produced.

[0003]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and provides a method and apparatus for treating sewage capable of preventing generation of scale for a long period of time even when treating water having high hardness. The challenge is to provide.

[0004]

In order to solve the above-mentioned problems, the present invention provides a wet oxidation treatment method for wastewater, in which organic pollutants in wastewater are oxidized and decomposed by adding an oxidizing agent under high temperature and pressure, The oxidation treatment is performed using a metal reactor, an inner wall of the reactor is used as an anode, a cathode is provided so as to face the anode, and a DC voltage is applied between the negative and positive anodes so that the electrolytic current is constant. It was decided. In the above treatment method, when the applied voltage rises to a predetermined set value, it is preferable to apply an opposite voltage between both electrodes at the same electrolytic current for a certain time. Further, in the present invention, in a wet oxidation treatment apparatus for sewage that is oxidatively decomposed by adding an oxidizer under high temperature and pressure, a cylindrical metal reactor is used, and a mesh-shaped cylinder facing the inner wall of the reactor is used. An electrode is provided and a DC power source is connected to the reactor and the cylindrical electrode.

In the processing apparatus, the metal reactor is
It is preferably made of metallic titanium, or has metallic titanium internally stuck to the inner wall, or has platinum plated on the inner wall, and the cylindrical electrode has a metallic titanium substrate plated with platinum. What you did is good. The smaller the distance between the inner wall of the reactor and the anode, that is, the distance between the electrodes, the lower the voltage, but there is a risk of clogging by suspended solids, so about 3 to 10 mm is desirable. As described above, the present invention prevents generation of scale by making the inner wall of the reactor an anode and using a constant current power source to constantly supply a constant anode current to the anode. That is, under high temperature pressure, in the wet oxidation treatment method of sewage that oxidizes and decomposes organic pollutants in sewage by adding an oxidant, the inner wall of the cylindrical metal reactor is used as an anode, so that it faces the anode. By providing a mesh-shaped cylindrical cathode and applying a DC voltage between the negative and positive electrodes so that the electrolytic current is constant, scale is prevented.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
When supplying a constant anode current in the inner wall of the reactor using a constant current power supply, water anodic dissolution reaction of the following _{(1) H 2 O --- →} 2H + + 1 / 2O 2 + 2e - (1) with hydrogen Since ions are generated, the acidity of the thin film of the liquid in contact with the inner wall of the reactor, that is, the liquid boundary film can be maintained higher than that of the water to be treated inside. On the other hand, it is considered that the mechanism of scale formation due to the temperature rise of the water to be treated is mainly due to the decrease in the solubility of calcium carbonate with the temperature rise, and the precipitation reaction is as shown in (2) below. Ca ²⁺ + CO ₃ ² -----> CaCO ₃ ↓ (2)

However, in a liquid boundary film having a high acidity, the following bicarbonate ion forming reaction (3) CO ₃ ²⁻ + H ⁺ −−− → HCO ₃ ⁻ (3) proceeds, and as a result, the reaction Precipitation of calcium carbonate due to the reaction (2) on the inner wall of the vessel is suppressed. Furthermore, once the calcium carbonate deposited on the inner wall of the reaction below _{(4) CaCO 3 ↓ + H} + --- → Ca 2+ + HCO 3 - (4) by dissolving and removed. In addition to the dissolving action by the reaction (4), the peeling action of the scale by the oxygen gas generated by the reaction (1) is also effective. However,
Scale deposition is unavoidable on the surface of the cathode according to the invention. Therefore, the electric resistance on the cathode surface increases with the scale deposition on the cathode surface, and a constant electrolytic current (anode current)
In order to maintain the above, the applied voltage, which is the output voltage of the constant current power supply, rises.

According to the present invention, when the applied voltage rises to a predetermined set value, an opposite voltage is applied for a certain period of time at the same electrolytic current between both electrodes. The scale produced on the surface of the cathode by this is dissolved and peeled by the reaction (1) and the reaction (4) to be removed. Then, the application of the positive voltage is restarted after a lapse of a predetermined time of the application of the reverse voltage.
The electrolysis current may be 0.1 milliamper or more per square centimeter of the inner wall area of the reactor, that is, the electrolysis current density may be 1 mA / cm ² or more, preferably 0.5.
The range of up to 5 mA / cm ² is desirable. Most of the electrolytic energy consumed by the present invention is converted into thermal energy and is effectively used for heating or maintaining the temperature of the water to be treated, so that the running cost does not increase. From the viewpoint of conductivity and corrosion resistance, the inner wall material of the reactor is preferably a stainless steel base material plated with platinum, or a metal titanium or metal titanium base material plated with platinum.

The mesh-shaped cylindrical electrode mounted inside the reactor is preferably metal titanium or a metal titanium base material plated with platinum or a stainless steel base material plated with platinum. It goes without saying that aqueous solution treatment under subcritical or supercritical conditions is also within the scope of the present invention. Next, the present invention will be described with reference to the drawings. FIG. 1 shows an overall configuration diagram of the processing apparatus of the present invention. In FIG. 1, reference numeral 1 is a cylindrical metal reactor, which is provided with a mesh-shaped cylindrical electrode 2 facing the reactor 1, and the reactor 1 and the cylindrical electrode 2 are connected to a constant current power source 3. Therefore, a constant current is applied during the oxidation process. And 4 is a stirrer,
5 is a lid.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 The apparatus used for the experiment is shown in FIG. The reaction vessel of the autoclave used was cylindrical and had an internal volume of 300 ml.
The material was titanium plated with platinum. The electrode provided as a cathode had a cylindrical mesh shape, and the material was titanium plated with platinum. The distance between the reaction container and the cathode was 4 mm. The water to be treated has a calcium hardness of 250 mg / liter and a total alkalinity of 2
Calcium chloride and sodium hydrogencarbonate were added to tap water and used so that the concentration would be 00 mg / liter.
At the same time as 250 ml of the water to be treated was placed in a reaction vessel to raise the temperature, a current of 150 mA (anode current density of 2 mA /
It was the start of a constant current electrolysis of cm ^2). It was heated at a constant temperature rising rate and kept at 200 ° C. for 40 minutes. Changes in voltage and conversion of electrolytic polarity during this period are shown in Table 1 below.

[0011]

[Table 1]

After 100 minutes, the electrolysis was stopped and the autoclave was cooled. After that, the reaction vessel and the cathode were taken out and the surface was observed, but no scale adhesion was observed. On the other hand, for comparison, a comparative experiment was conducted under the same conditions as the above experiment except that electrolysis was not performed. After the experiment, the reaction vessel and the cathode were taken out and the surface was observed, but both had white scales attached.

[0013]

According to the present invention, the problem of scale formation on the inner wall of the reactor in the wet oxidation process can be solved by the above-described simple method and apparatus.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a processing apparatus of the present invention.

[Explanation of symbols]

1: Reactor, 2: Cylindrical mesh cathode, 3: Constant current power supply, 4: Stirrer, 5: Lid

Continuation of front page (56) Reference JP-A-9-94584 (JP, A) JP-A-7-185540 (JP, A) JP-A-6-328085 (JP, A) JP-A-6-277679 (JP , A) JP 6-262188 (JP, A) JP 6-91280 (JP, A) JP 56-129085 (JP, A) Actually open 3-66700 (JP, U) Actually open 57-5899 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 1/74 C02F 1/461 C02F 5/00

Claims (5)

(57) [Claims] 1. A method for wet oxidation treatment of wastewater, wherein organic pollutants in wastewater are oxidatively decomposed by adding an oxidant under high temperature and pressure, wherein the oxidation treatment is carried out using a metal reactor. The method for treating sewage is characterized in that a cathode is provided so that the inner wall of the anode is an anode and the cathode faces the anode, and a DC voltage is applied between the cathode and the anode so that the electrolytic current is constant. 2. The treatment method according to claim 1, wherein when the applied voltage rises to a predetermined set value, an opposite voltage is applied between both electrodes at the same electrolytic current for a certain period of time. Method. 3. In a wet oxidation treatment apparatus for wastewater, which oxidizes and decomposes by adding an oxidant under high temperature and pressure, a cylindrical metal reactor is used, and a mesh-shaped cylindrical electrode is arranged so as to face the inner wall of the reactor. And a DC power source connected to the reactor and the cylindrical electrode. 4. The metallic reactor is made of metallic titanium, has metallic titanium internally attached to its inner wall, or has its inner wall plated with platinum. Item 5. The wastewater treatment device according to item 3. 5. The sewage treatment apparatus according to claim 3, wherein the cylindrical electrode is formed by plating platinum on a metallic titanium base material.